Can I become happy by association?

Should I associate with happy people because they make me feel good by association, or unhappy people because they make me feel good by comparison? Or do economists claim that I should be indifferent?
D.K., New York

Dear D.K.,

Economic theory makes no such claim: it insists merely that your preferences be consistent and complete because that makes the mathematics easier. Although many economic models concentrate on your demand for physical goods, that is merely to keep things simple. There is no theoretical reason to insist that your happiness cannot depend on the happiness of others.

Your question, then, should be addressed empirically, and a fascinating new paper in the British Medical Journal tries to do just that. The authors, James Fowler and Nicholas Christakis, find that happiness is contagious.

If just a single nearby friend becomes happy, your chances of being happy rise by a quarter. Physical proximity seems to be important, and happiness is far more contagious among people of the same sex.

This has a ring of plausibility, yet there are some curious results – for instance, that a happy next-door neighbour seems to affect your mood more than a happy spouse. Meanwhile, in another BMJ study, Jason Fletcher and the economist Ethan Cohen-Cole use a similar data set and methodology to demonstrate that height also seems to be contagious, which seems rather unlikely.

The trouble is that it is hard to separate genuine contagion from other effects – such as a shared physical environment, or people befriending others who seem similar to them. My recommendation: by all means seek out happy people, but do not expect miracles.